Acid‐Induced Rearrangement of Epoxygermacra‐8,12‐olides: Synthesis and Absolute Configuration of Guaiane and Eudesmane Derivatives from Artemisiifolin

Abstract

A study on the acid‐induced rearrangement of 4,5‐epoxy‐ and 1,10‐epoxygermacra‐8,12‐olides was carried out. From a 4,5‐epoxy derivative, guaianes were obtained, whereas 1,10‐epoxy derivatives furnished, depending on the stereochemistry of the C‐1/C‐10 epoxy ring, trans‐5β,10α‐ or trans‐5α,10β‐eudesmanolides.

2α-Acetoxy-15-acetylartemisiifolin, a new Anti-trypanosomal Sesquiterpene Lactone from Mikania guaco

“…The location of the two acyl groups at C-2 and C-15 were deduced from the chemical shifts of H-2 (6.27) and H- 15 Also, the low shifted H-2 (at δ 6.27) was supported by HMBC correlation with C-3 and C-4, as well as the coupling constant which is typical of 2 orientation (J 23 =11.1 Hz, J 23 = 5.4 Hz) [14]. The chemical shifts of the exomethylene group (H-13) at δ 6.20 and δ 6.31 are in agreement with the more stable C-8 lactonized isomer [18] and their chemical shift is very similar to that of artemisiifolin and other C-8 lactonized isomers reported previously [19,20]. The relative configuration of 1 was established using 2D-NOESY experiments.…”

Sesquiterpenoids from Common Ragweed (Ambrosia artemisiifolia L.), an Invasive Biological Polluter

“…Artemisiifolinic acid ( 15a ) is closely related to artemisiifolin, a compound isolated from an American collection of A. artemisiifolia ,25 from which it differs in the oxidation of Me‐14 to a carboxylic acid and in the hydrogenation of the Δ 1,10 double bond. The 1 H NMR spectrum of 15b was, however, characterized by sharp and well‐defined signals, showing a substantial difference from the conformational behavior of artemisifolin, a mixture of slowly interconverting rotamers at room temperature 26…”

Structural Determination of Complex Natural Products by Quantum Mechanical Calculations of ¹³C NMR Chemical Shifts: Development of a Parameterized Protocol for Terpenes

“…In order to reduce the computational costs in our calculations, we parameterized the scaling factor using sesquiterpene molecules, a sub-class of terpenes with structural frameworks containing only 15 carbon atoms. 13 A set of 10 sesquiterpene molecules (figure 1), whose structures have been reliably elucidated in literature, [14][15][16][17][18][19][20][21][22][23] were selected and submitted to randomized conformational searches using Monte Carlo method and MMFF force field. The most significant conformations of each compound, considering an initial energy cutoff of 10 kcal.mol -1 , were selected to single-point energy calculations at the B3LYP/6-31G(d) level of theory.…”